Light Emitting Diodes (LEDs) and Organic Light Emitting Diodes (OLEDs) have enjoyed a rapid development in the past couple of decades and have started to replace existing lighting and display devices. Due to the specific device structures of LEDs and OLEDs, significant portion of the light generated inside the active region is totally reflected at various interfaces and is “trapped” inside the device, leads to reduced efficacy of the light emitting device.
The problem is particularly severe for OLED given the technology is in a much early development stage than its LED counterpart. For example, only ˜20% of all the photons generated in an OLED lighting device are extracted out. Many light extraction schemes have been applied to LEDs and OLEDs, such as backside reflector, high refractive index encapsulant, surface roughening or surface texturing, etc. Textured extraction film is a popular solution for OLED lighting as it is compatible with the roll-to-roll manufacturing process and can be easily applied on either side of the final encapsulation layer.
A pedagogical depiction of the device structure of a typical OLED device with textured surface is shown in FIG. 1. The active area (101) emits light, for both a top emitting and bottom emitting device structure, through a transparent conductor, such as an Indium Tin Oxide (ITO), layer (102) and the substrate (103), which is surface textured (104) to reduce the light loss due to total internal reflection at the substrate/air interface.
In an Active Matrix OLED (AMOLED) display, however, due to pixelated nature of the active region, the surface texture degrades the optical quality of the pixels, creating an undesirable blur effect.
In one aspect of this invention, we describe a light extraction structure that can be placed immediately on top of, or in close vicinity, of the active region, is described. Such a structure can improve the light extraction of the AMOLED display and at the same time preserve the optical quality of the pixels.